Builder demanding extra Money against the Registered agreement

I had purchased a 2 BHK flat in Kandivali in 2005 through a reputed builder and got the flat registered by paying the stamp duty. I have already paid 60% of the cost of the flat and had taken a loan from a Bank.
The agreement was signed by me and the builder’s representative.
Thereafter in 2006 the work was stopped due to the forest case. Supreme court had passed a judgement in 2014 to remove the forest land tag and now in 2016 finally all the land has been cleared by Supreme court.
In July 2016 I get a letter from the builder advising that as there is an escalation in cost I am requested to visit the Builders office and discuss the same.
On visiting the builders office I was handed over a Letter of Understanding which had mentioned the below points and was requested to sign the same.
A) Increase of 3000 per sq ft as per the agreed registered copy
B) Additional infrastructure development 600 per sq feet
C) Additional Clubhouse charge lumpsum 4 Lacs, where as in the registered agreement copy it was mentioned as 20,000 per year at the time of possession.
D) The Total 100 % extra amount of 25 Lacs to be paid within 60 days after the recommencement of the work.
E) I agree, I do not have any problem if the builder constructs future buildings with the FSI allocated for my building.
F) I agree, to sign the supplement agreement copy and pay the govt taxes.
G) I agree that I shall not go to the court or take any legal action against the builder incase of any modification of the plan, delay in giving possession etc
(These are some of the points which I had noted in my diary as I was not given a copy)
The customer service manager advised that I would not get any copy of the Letter of Understanding which was addressed to the builder and Signed by me.
I was advised that this Letter of Understanding is just a letter to the builder and does not hold any legal value as it is not a stamp paper, it is only so that he knows that I agree with the builders terms as he now intends to restart with the project and does not want even one single buyer to cause trouble.
I advised the service manager that I would not sign the copy and did not agree to pay the extra 25 lacs.
Please advise me on the below following points
1) Does the letter of Understanding signed by me have any legal standing and could I take legal action against the builder once I sign it.
2) Can the builder cancel my registered flat for which I have paid 60% and sell it off to another buyer.
3) Is a Supplementary Agreement copy legal and does it supersede the earlier Agreement.
4) Can the builder refuse to hand over the possession of the Flat to me if I only pay the balance 40% of the registered agreement with the additional maintenance and govt taxes.
Kindly advise what recourse of action should I take as I am presently staying with my parents.
Regards,
Kumar

Indian Laws

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